The Applicants have previously proposed in U.S. application Ser. No. 558,714 a type of apparatus in which a choke valve within an inlet passage of an internal combustion engine is provided on one side thereof with a pulse motor connected thereto and connected to a drive pulse circuit, so that the valve is controlled according to engine temperature by driving the pulse motor by an output pulse signal from the circuit, which corresponds to engine temperature.
In the aforesaid application, a pulse generator constituting the drive pulse circuit is constructed as a variable frequency type oscillator whose oscillation frequency is varied by a temperature sensitive type variable resistor which varies in resistance value according to engine temperature. However, with this arrangement, the pulse motor must be a variable speed type motor whose output speed of revolution is varied according to change of input pulse frequency. This type of motor is comparatively expensive.